Illinois legislation is advancing that would regulate decades-old but debated technology used to reach previously inaccessible natural gas reserves deep underground.

The state Senate on Thursday unanimously sent to the House a bill addressing hydraulic fracturing, or fracking. That technology involves using mixtures of water, sand and chemicals to free below-ground energy reserves.

The Senate bill comes as energy companies are pushing to prospect possible drilling sites using fracking in southern Illinois.

The legislation would allow the state's Department of Natural Resources to regulate fracking. It also would require energy companies to publicly disclose the chemical composition of the fluids used and test the integrity of the cement and steel well casings meant to protect groundwater during drilling.

Environmentalists are guarded about the technology because of possible pollution.